Diesel oil, due to its cost and availability, continues to be the backbone for industry around the world being the principal fuel for use in trucks, ships, trains, some cars and other automotive equipment and different stationary types of engines. In this respect, it is well recognised that any commercially acceptable diesel or diesel blend must be capable of performing over a range of prevailing climatic conditions and to achieve this it must maintain a single phase. Typically, such single phase must be maintained at temperatures of 0.degree. C. and above.
It is also well recognised that the combustion of diesel fuel in engines can be hazardous to the environment, In particular, the partial combustion of diesel fuel to carbon, carbon monoxide, and nitrogen oxides creates noxious black exhaust gases which are pollutants. This problem is particularly observable in trucks and other automotive vehicles where noxious black exhaust gases can be seen being released into the environment.
Attempts have been made over the years to address the environmental concerns associated with exhaust fumes from engines by using alcohols such as methanol (methyl alcohol) or ethanol (ethyl alcohol) as fuels. Such attempts, for instance, have generally established that 15% of ethanol and 85% diesel oil provides an acceptable burning capacity without the necessity of modifying existing diesel engines.
The problem with using alcohols from methanol up to n-propanol as a fuel in conjunction with diesel oil is that they are immiscible with diesel oil, that is, they cannot be uniformly mixed or blended into one phase without rapid separation into their component parts. Since they cannot be uniformly mixed into one phase and stored for easy use, the components must be mixed just prior to use by, for example, having independent fuel tanks with the components independently pumped and mixed just before the combined fuel is injected into the fuel chamber, Such a system is currently being used in the bus fleet of the Des Moines Transit Authority, Iowa, USA,
Alcohols above amyl alcohol are miscible with diesel fuels and therefore the problem does not arise. However, the lower alcohols, especially ethanol, are clearly preferred over such higher alcohols. For example, ethanol is a low cost alcohol which can be derived from natural renewable resources, even from the fermentation of waste streams.
Accordingly, one attempt to address the problem of immiscibility was made to form an emulsion of the diesel oil and ethanol using an emulsifier. An example of this is in Australian Patent No. 544,728 (Apace Research Ltd) which discloses a composition having 84.5% diesel oil, 15% hydrated ethanol and 0.5% emulsifier. The emulsifier is of the styrene butadiene co-polymer type in admixture with a high molecular weight polyethylene glycol dissolved in xylene. This mixture can show both batch to batch variation and instability as the diesel and ethanol separate in the fuel tank.
An attempt has also been made to address the problem of immiscibility by forming a blend comprising a petroleum fuel, methanol and a higher alcohol having 10-16 carbon atoms as a solvent for the petroleum fuel and methanol. An example of this is disclosed in U.S. Pat. No. 4,527,995 (Itow),
A further attempt to address the problem of immiscibility is disclosed in UK Patent No. 2,090,61 1 (Guibet) where combustible compositions contain gas oils, methanol and a fatty acid ester for use in diesel engines. It refers to the use of other heavier alcohols to assist the miscibility of methanol in gas oil but observes that these are commercially unacceptable. The use of fatty acid esters is proposed to overcome the immiscibility between methanol and gas oil. From the examples, the percentage of fatty acid ester required to solubilize methanol is always significantly in excess of the percentage of methanol.
The article entitled "Diesel Oil Substitution by Processed Plant Oils--Engine and Vehicle Results" published in 1982 by two authors from Volkswagon do Brasil S.A. Brazil, compares tests conducted using a straight methyl ester of soya bean oil (MESO) as a fuel with a 75-25 gas oil-MESO blend and a 68-23-9 gas oil-MESO-ethanol (anhydrous) blend. The article provides that plant-oil mono-esters used as gas oil extenders serve as co-solvents between gas oil and ethanol, thus permitting ready use of otherwise-incompatible ethanol. However, the article provides that an increase in proportion of ester in the gas oil from a 20 to 25% ester content onwards results In the ethanol being substantially compatible in the gas oil. Therefore, a significantly greater amount of ester than ethanol is necessary to achieve a miscible composition.
Another fuel composition is disclosed in the 1920's U.S. Pat. No. 1,423,049 (Tunison). This patent discloses a fuel mixture of petroleum distillate (heavier than kerosene) and an ester of an organic acid and a mono-hydric alcohol, In a preferred form, alcohol is added although in the rest of the specification there is no working example or other explanation of specific alcohols. The prime interest of this patent is the incorporation of the ester of an organic acid and of the mono-hydric alcohol. The volatile which may be present may be alcohol or other volatile eg. ketones. The specification states that a wide range of alcohols are miscible with the heavy oil. However, it is well known that alcohols from methanol to n-propanol are immiscible with today's diesel oil and/or gas oil. It would seem that the heavy oil specified is not the diesel oil of today and the patent is not directed to the particular immiscibility problems of methanol to n-propanol with diesel oil and gas oil.
An attempt at substantially substituting alcohols for diesel fuel is disclosed in U.S. Pat. No. 4,405,337 (Mori). This patent specifies castor oil, which is the only hydroxy fatty acid based vegetable oil, as the means which permits the maximisation of the use of alcohol in the fuel and minimisation of the gas oil volume. The patent also teaches that only castor oil can be mentioned as a vegetable oil capable of dissolving alcohols therein. Castor oil is A triglyceride and each fatty acid chain contains a hydroxyl group which may be the reason for it assisting the solubility of ethanol in itself and thence in diesel fuel.
In subsequent investigations leading to the present invention, it has surprisingly been found that the hydrocarbon liquid and ethanol and/or n-propanol can be caused to form a single phase composition which is not prone to separation. In particular, it has been found that non-hydroxy fatty acids and/or organic esters having up to 15% by volume in the fuel blend composition can function as coupling agents between these compounds.